The invention relates generally to the field of power over local area networks, particularly Ethernet based networks, and more particularly to a method of detection and determination of a type of powered device attached over four twisted wire pairs.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The structure cable is also known herein as communication cabling and typically comprises four twisted wire pairs. In certain networks only two twisted wire pairs are used for communication, with the other set of two twisted wire pairs being known as spare pairs. In other networks all four twisted wire pairs are used for communication. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to; reduced cost of installation; centralized power and power back-up; and centralized security and management.
The IEEE 802.3af-2003 standard, whose contents are incorporated herein by reference, is addressed to powering remote devices over an Ethernet based network. The above standard is limited to a powered device (PD) having a maximum power requirement during operation of 12.95 watts. Power can be delivered to the PD either directly from the switch/hub known as an endpoint power sourcing equipment (PSE) or alternatively via a midspan PSE. In either case power is delivered over a set of two twisted pairs. Unfortunately, no provision has been made in the above standard for PDs requiring power in excess of the above maximum power requirement. The above mentioned standard further prescribes a method of classification having a total of 5 power levels of which classes 0, 3 and 4 result in a maximum power level of 15.4 at the PSE which is equivalent to the aforementioned 12.95 watt limit.
The IEEE 802.3 at Task Force has been established to promote a standard for delivering power in excess of that described in the aforementioned standard. Two basic approaches for increasing power exist:
1) increasing the amount of power delivered over a single set of two twisted wire pairs as compared to the power limits of the above IEEE 802.3 af standard; and
2) delivering power over two sets of two twisted wire pairs. For simplicity, a powered devices arranged to receive power in accordance with the IEEE 802.3 af standard, i.e. at power levels on the order of a maximum of 12.95 watts with power being delivered over a single set of two twisted wire pairs is hereinafter denoted an 'af device or an 'af PD. A PD arranged to receive power in excess of 12.95 watts, or is operational in accordance with a standard which allows for power significantly in excess of 12.95 watts is called hereinafter a high power PD.
Delivering power over all four twisted wire pairs, i.e. over two sets of two twisted wire pairs of the communication cabling requires careful attention to a number of possible connection combinations. In particular, the PSE is not a-priori aware of the actual device connected, and therefore detection and classification must detect and determine a possible non-powered device, an 'af PD which is connected with a diode bridge input allowing for powering over either set of two twisted wire pairs, a high power PD receiving power over both sets of twisted wire pairs, and a high power PD receiving high power over either set of two twisted wire pairs. In an exemplary embodiment a high power PD arranged to receive power over a single set of two twisted wire pairs is powered at a higher voltage than an 'af PD.
In an exemplary embodiment a high power PD receiving power over all four twisted wire pairs is provided with a combiner as described in pending U.S. patent application Ser. No. 10/761,327 filed Jan. 22, 2004 entitled “High Power Architecture for Power Over Ethernet” whose entire contents are incorporated herein by reference. Such a combiner exhibits a detectable signature impedance at the input for each set of two twisted wire pair connections receiving power.
Several patents addressed to the issue of supplying power to a PD over an Ethernet based network exist including: U.S. Pat. No. 6,473,608 issued to Lehr et al. and U.S. Pat. No. 6,643,566 issued to Lehr et al. the contents of both of which are incorporated herein by reference.
A PSE is a power sourcing equipment arranged to power a specific PD over a specific link. Thus, in an 'af environment a single PSE is associated with a single PD. In a high power environment, a number of options exist, including powering a single PD from a plurality of PSEs. For the sake of clarity, for the purposes of this document the term Powering Source (PS) is used to mean a single powering source designed for connection to a single set of twisted wire pairs. Thus, a high power PD may be arranged to receive power from a single PS over a single set of two twisted wire pairs, or from two PSs over two sets of twisted wire pairs. Functionality, such as detection and classification may be separately supplied to each PS, or may be shared among the PSs by a single controller.
It would therefore be desirable to have an architecture enabling powering remote devices over an Ethernet network having high power needs, and preferably having a method operable to detect and identify a possible 'af PD which is connected with a diode bridge input allowing for powering over either two twisted wire pairs, a high power PD received power over both twisted wire pairs, and a high power PD receiving high power over either two twisted wire pairs.